Rear diff weirdness

[Subourbon]

Hey guys,

K20 1982 3/4 ton 6.2 v8 diesel
Decided to change oil in diffs today. Only had time to do rear.

Despite being careful the gasket tore and jt leaked. So silicone and now she's drying up.

Onto the question... my rear diffs fill plug, it has a narrow 1/4 " diameter tube about 2 inches tall, and a rubber hose coming out of it and up to a plugged end bolted To a bracket on the body... see pics. What on earth is that? Is that to fill it from a more comfortable position?

Then plastic plug at the plugged end looks like it can come off and I tried butnit felt fragile and indidnt want to break it...
Anyways the entire length of the hose is about 2 feet maybe which tells me you could fill by feeding the hose through the wheel arch and do it from a more comfortable position... is that the only apparent goal, has anyone seen this before?

I didnt see it in the Haynes squarebody or 6.2 diesel manuals...
Sorry for the blurriness.

You see the hose clamp holding the rubber hose to the fitting that... honestly I didn't want to damage it by seeing if it was threaded in or whatever. I jist bypassed the hose and filled it with my gallon hand pump and clear hose.... then it leaked. Anyways....

Who has seen this before? And what do you guys have as a fill plug?

 

[Turbo4whl]

That is the axle vent.

 

[mtnmankev]

Look at the passenger side of the front part of the differential for a fill plug.
A 3/8" square drive will fit it.

 

[Subourbon]

Axle vent, that's what I thought, so that plastic tip then is like a screen prevent dirt n crap getting in and just breathe to equalize to atmospheric pressure as the fluid moves around... a.k.a a vent. Lol ok cool good to know

 

[Subourbon]

I thought I saw a 3/8 drive plug and then saw that line with the vent. So tomorrow I should fill through there and not through the vent, that 3/8" drive plug is my fill as well as tell tale for when it's full, correct?

 

[mtnmankev]

Yes, with the truck sitting level, fill until it just barely starts to run out the hole.
And, as a general rule I was taught back in the 1960's, if you can stick your pinky in the hole, aim downwards, and you have gear oil touching the finger close to the first joint, you have plenty of oil in it and there is no danger of it running dry or being damaged.

 

[Subourbon]

Awesome good tip, i saw that one on a YouTube video.
Never heard any mention of a vent line when I was watching how to videos, it makes sense that there is one. So, are vent lines a thing of the past, built into diffs differently? Just find it strange with all the home mechanic youtube videos not a single one I watched mentions it
I was gonna do my front diff too but woth the gasket tearing ill have to run out n get more oil before attempting that....
Butni had heard of the pinky trick! Thanks for the advice much appreciated.
I'm pretty level. Despite being tempted to jack it up a bit, it's snug under there.

 

[Subourbon]

What prompted the diff oil change was, at low speed when reversing, there is a knocking, kinda like with hot brake discs on an old car in stop n go traffic on a hot day just a bit louder. I can't really explain how else it sounds.
It's not the trans. It sounds like it comes from the rear end, like rear diff and drive shaft area.
I always reverse into my spot, and when reversing I hear it, then pull forward to straighten out, I hear it going forwards too.
But when I fire up in the morning and pull away, i dont hear it, it's like reversing prompts the noise, then it does it going forwards... once i get it up to road speed it's fine...

When i did my oil change on the diffs i didnt notice anything the gears looked fine, rinsed the thing with brake cleaner, wiped it clean.
Plus I tore the gasket on the rear diff and had it almost filled up with fresh oil and dumped it to add gasket maker to my diff cover, so it's had a "flush" with clean oil.

I'm curious if there's a maintenance to the drive shaft, like grease nipples I'm missing or is it "normal" coz it's pretty old stuff any insight from you guys as usual is appreciated!

 

[Grit dog]

If the u joints are grease-able then yes. If not then no.
I’ve always found greasing u joint to be hit and miss in the success department. Fine if new(er) or regularly maintained but it always successful at getting grease to all 4 cups if they’re older and haven’t been greased periodically.

 

[Subourbon]

Alright, I dodnt really notice anything under there. Bjtnthen again I wasn't looking for it either.
Just a general all purpose grease or is there a specific one hat is better or recommended?

 

[Radiohead]

I would also be curious to see how much play there is in the pinon to ring gear. Something else to consider/inspect for searching the cause of the noise.

 

[Subourbon]

You mean the backlash? So I'd have it in jackstands doff cover off and wiggle it around and check the play with a dial gauge?
Wouldn't that just bang in when I engage forward or reverse, after theyre meshed in, I wouldn't be able to hear the clunking... theoretically. I dunno. I need to be a fly on the wall in a lot of places to be sure. And it very well could be that. It's an 82 I've owned for 4 years. It's got long history before I had it. I dunno when those things were checked or changed.
But that's something I'll check next time I have the chance. Found a leak in my radiator today. Yay.

 

[rusted nuts]

You mean the backlash? So I'd have it in jackstands doff cover off and wiggle it around and check the play with a dial gauge?
Wouldn't that just bang in when I engage forward or reverse, after theyre meshed in, I wouldn't be able to hear the clunking... theoretically. I dunno. I need to be a fly on the wall in a lot of places to be sure. And it very well could be that. It's an 82 I've owned for 4 years. It's got long history before I had it. I dunno when those things were checked or changed.
But that's something I'll check next time I have the chance. Found a leak in my radiator today. Yay.

Drum brakes on rear?? May want to check them out.

 

[ChuckN]

If the u joints are grease-able then yes. If not then no.
I’ve always found greasing u joint to be hit and miss in the success department. Fine if new(er) or regularly maintained but it always successful at getting grease to all 4 cups if they’re older and haven’t been greased periodically.

Not to hijack here- but the front driveshaft zerk fitting on my C10 is really hard to get to, my grease gun won’t fit in there to lube it. Any tricks? I rotated the driveshaft to see if the I could get more space but doesn’t seem to help. Thanks in advance.

Sorry again to go off topic, this thread just brought it to the front of my brain.

 

[Rusty Nail]

How much bourbon did you drink prior to creating this masterpiece of a post?
Do you drink bourbon while playing with the truck or only while driving it?

Did you think it was a vent or did you think it was "for a more comfortable position to fill it up from"? Cuz you said both and that's probably how I got confused.

You filled it up through the hose AND THEN it started leaking? Man that IS weird! You're right.


More importantly ,what kind of bourbon do you like the best?